1. Field of the Invention
The present invention relates to a projection display device for projecting an image on an imager onto a projection plane, and more particularly, is suitable for use in a projection display device for enlarging and projecting projection light from an oblique direction.
2. Description of the Related Art
A conventional projection display device (hereinafter referred to as “projector”) is configured to project projection light from an optical engine onto a screen through a projection lens. Meanwhile, there has been proposed a method of reflecting light from a projection lens by an aspherical mirror to increase a spread angle of the projection light. According to this method, projection light is projected onto a screen surface from an oblique direction as shown in FIG. 14, thereby reducing space required for travel of the projection light.
In a projector of this kind, as a throw distance (H0) shown in FIGS. 14A and 14B becomes smaller, space required for travel of projection light is reduced. This decreases a possibility that the projection light is blocked by an obstacle or the like.
When a person makes a presentation with reference to an image projected onto a screen in a usage pattern shown in FIG. 14A, for example, the smaller the throw distance (H0) is, the more the possibility for the projection light to be blocked is decreased, and the less a projection image is prone to be darkened by shadow. Therefore, the presenter can smoothly make a presentation at a position closer to the screen. Similarly in a usage pattern shown in FIG. 14B, as the throw distance (H0) is smaller, there is a more lowered possibility that the projection light is blocked by person(s) around a desk or object(s) on the desk. This provides a user with higher operability and value in use.
As foregoing, decreasing the distance (H0) from a projection plane (screen surface) to a projection light emitting position improves the ease-of-use of a projection display device.